Elimination of unfavorable outflow margin

ABSTRACT

A panel for use in a gas turbine engine exhaust case is disclosed. The panel has an airfoil section and a flow diverting structure adjacent a leading edge, wherein the flow diverting structure directs fluid flow into an area of the airfoil that lacks sufficient internal pressure for cooling fluid flow.

STATEMENT OF GOVERNMENT INTEREST

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of ContractNumber N00019-02-C-3003 awarded by United States Navy.

BACKGROUND

This invention relates generally to gas turbine engines and moreparticularly to elimination of unfavorable outflow margins in turbineexhaust cases.

For particular operations, particularly in military operations, it isdesirable to have aircraft with conventional take-off and landing (CTOL)capabilities, and short take-off vertical landing (STOVL) capabilities.CTOL requires conventional thrusting of the aircraft in the horizontaldirection, while STOVL requires thrusting of the aircraft in verticaland intermediate directions. Some dual capability aircraft designs thusemploy variable direction exhaust ducts for directing thrust produced bythe exhaust nozzle in both the horizontal and vertical directions.Variable direction exhaust ducts typically comprise multiple co-axialexhaust duct segments having angled junctions, whereby the segments canbe rotated with respect to each other to redirect the direction ofthrust.

In STOVL applications, the lift-fan and roll-posts and the exhaustnozzle work in unison to develop vertical thrust in a powered-lift modeduring short take-off/landing segment of the flight (STOVL-PL). Theinternal engine modules that distribute the flow inside the engine aredriven by a dual-spool configuration with high and low-pressureturbines. After the low pressure turbine, the turbine exhaust case (TEC)is one of the last modules in the engine and functions to condition thegas flow before exiting through the exhaust, in either power-lift(STOVL-PL) or during augmentation at up-and-away (STOVL-UAA) flightmodes.

In current designs, TEC panels have a local outer region which lackssufficient internal static pressure for the air flow to discharge intothe external gas path via film cooling holes that characterize local TECdesign porosity. In turn, insufficient internal pressure leads to anegative outflow-margin in a critical region towards the TEC outerdiameter (OD) clockwise (CW) side of the panel. Externally, the gas flowapproaches the TEC airfoil at an angle that, upon impact, creates a “bowwave” that surrounds a region that covers the CW side of the vane withhigh external pressure levels. Simultaneously, if there are decrementsto the internal pressure levels, the internal-to-external pressuredifference decreases leading to an inflow condition or negative outflowmargin.

As the internal cooling flow passes through fan duct blocker in thesupply duct before turning into the TEC, a series of pressure dropsoccurs due to action of roll-post and fan duct blocker flow areavariation, particularly during powered-lift. This decreases TEC internalpressure leading to inflow conditions at the TEC critical areas, as isknown in the art.

Thermally, and as a consequence of negative outflow margin, the TECmetal temperatures increase to a point closely related to the materiallimit range of 645-705 degrees Celsius, depending on mechanical stress.This can lead to damage or failure of the TEC panel and airfoils, thusresulting in costly repair or replacement of the TEC panel. Thus, abetter system for cooling the critical areas of TEC panels is desirable.

SUMMARY

In one embodiment, a panel for use in a gas turbine engine exhaust casethat has a cooling bypass fluid flowing adjacent the exhaust case isdisclosed. The panel has an airfoil section and a flow divertingstructure adjacent a leading edge, wherein the flow diverting structuredirects cooling bypass fluid flow into an area of the airfoil that lackssufficient internal pressure for cooling fluid flow.

In another embodiment, a turbine exhaust case is disclosed. The turbineexhaust case has a forward outer diameter ring, a forward inner diameterring, an outer diameter case attached to the outer diameter ring, aninner diameter case attached to the inner diameter ring, a flame tubeattached to an aft end of the inner diameter case, and a plurality ofairfoils mounted between the inner diameter case and outer diametercase. A bypass cooling fluid travels adjacent the outer diameter case.At least one of the plurality of airfoils has a flow diverting structureadjacent the leading edge and the outer diameter ring. The flowdiverting structure directs bypass cooling fluid flow into an area ofthe airfoil that lacks sufficient internal pressure for cooling fluidflow.

In yet another embodiment, a method of reducing unfavorable outflowmargin in the cooling flow of a turbine exhaust case is disclosed.Turbine exhaust gases are directed to a plurality of hollow airfoilswithin the turbine exhaust case. A cooling bypass flow is directed to aradial outer side of the turbine exhaust case. A flow divertingstructure is provided adjacent a leading edge of one of the plurality ofhollow airfoils. The flow diverting structure directs fluid flow into anarea of the airfoil that lacks sufficient internal pressure for coolingfluid flow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a jet-powered aircraft in phantom havinga STOVL capable gas turbine engine.

FIG. 2 is a cross-sectional view of the turbine exhaust case of thejet-powered aircraft illustrated in FIG. 1.

FIG. 3 is perspective view of a portion of the turbine exhaust casecontaining several radial turbine exhaust case panels.

FIG. 3A is an perspective view of one of the turbine exhaust case panelsillustrated in FIG. 3.

FIG. 4 is an elevation view of a turbine exhaust panel with a novelarrangement of internal iso-grids.

FIG. 5 is a plan view of a turbine exhaust panel containing a fluidscoop.

FIG. 6 is a cross-sectional view of a turbine exhaust case with aturbine exhaust case panel that contains a fluid scoop.

DETAILED DESCRIPTION

FIG. 1 shows jet-powered aircraft 10 having short take-off verticallanding (STOVL) gas turbine engine 12. Engine 12 includes multiplethrust producing and thrust directing elements which enable aircraft 10to take-off on a shortened runway and land vertically. Engine 12includes lift fan 14, lift fan shaft 16, power plant 18, control ducts20A and 20B, turbine exhaust case 22, three bearing swivel duct 24 andexhaust nozzle 26. Power plant 18 is the primary thrust-producingelement of engine 12 and is used to produce thrust oriented in the xdirection. Power plant 18 contains a compressor, a combustor, and highpressure and low pressure turbine sections. Air enters the front ofpower plant 18, and a portion goes to both a bypass and into thecompressor. The compressor compresses the air and directs it into thecombustor, where it is mixed with fuel and ignited. The exhaust from thecombustor drives the turbine sections to produce thrust. Upon exitingthe turbine sections, the exhaust enters turbine exhaust case 22.

Three bearing swivel duct (3BSD) 24 directs the thrust of power plant 18in the x direction when in configuration A (as shown by 3BSD 24 in solidlines). 3BSD 24 is adjustable to redirect the thrust of power plant 18in the y direction when in configuration B (as shown by 3BSD 24 indashed lines). 3BSD 24 is also be used to produce thrust in intermediatedirections. Nozzle 26 increases and focuses the thrust produced by powerplant 18 and is secured to the tail end of 3BSD 24. 3BSD 24 is used inconfiguration A during traditional take off and flight operations ofaircraft 10 in the x direction. 3BSD 24 is positioned in intermediatedirections to facilitate short take-off operations. 3BSD 24 ispositioned in configuration B to assist lift fan 14 in vertical landingoperations.

Lift fan 14 is selectively driven by power plant 18 through lift fanshaft 16, and is used to produce thrust in the y direction near theforward portion of aircraft 10. With 3BSD 24 producing thrust near theaft portion of aircraft 10, lift fan 14 and power plant 18 control thepitch of aircraft 10. During vertical landing operations, control ducts20A and 20B redirect a portion of the thrust produced by power plant 18in the y direction underneath the wings, at a location away from theaxis on which power plant 18 and lift fan 14 produce thrust in the ydirection. Control ducts 20A and 20B are selectively engaged to balancethe roll of aircraft 10 during vertical landing and take-off operations.

FIG. 2 is a cross-sectional view of a portion of jet-powered aircraft 10illustrated in FIG. 1 including turbine exhaust case 30. Turbine exhaustcase 30 includes turbine exhaust case (TEC) panel 32 between innerdiameter case 32 and outer diameter case 36. Panel 32 is a hollowairfoil constructed from sheet metal, composites, ceramics or similarmaterials known in the art. Panel 32 contains a series of iso-gridsupports 38 on the interior surfaces that provide structural support forpanel 32. Inner case 34 is connected to inner ring 40, and outer case 36is connected to outer ring 42. Inner case 34, outer case 36, inner ring40, and outer ring 42 are all constructed from metal made to withstandthe temperatures of exhaust gases leaving the turbine.

Tie rods 44 secure the turbine exhaust case to the rest of the engineassembly. Turbine exhaust case 30 supports aft bearing 46 of the enginethrough bearing support 48. Exhaust gases E leave last turbine stage 50and enter turbine exhaust case 30. At the opposite end of turbineexhaust case 30, augmentor spray bar 52 may be attached adjacent panel32, which along with flameholders, are axially located between theturbines and an exhaust nozzle at a downstream end of the combustionzone for injecting additional fuel when desired during reheat, thrustaugmentation, or afterburning operation for burning in the augmentorcombustor for producing additional thrust.

Radially outward of turbine exhaust case 30 and outer engine case 54 isbybass flow passage 56. Bypass flow fluid F, typically air, enters thefront of power plant 18 and travels adjacent the compressor and turbinesand is bled off to cool the various components of engine 12. Fluid F isalso used to cool the components of turbine exhaust case 30, includingpanel 32. Typically, air enters panel 32 and flows through the hollowairfoil between the iso-grids 38. Fluid then exits cooling holes inpanel 32 to create a film cooling effect on the outer surfaces of theairfoil of panel 32. A local outer area, depicted by line 58, is acritical area requiring cooling. To assure adequate cooling fluid flowin the area, a flow diverting structure may be installed adjacent thisarea.

FIG. 3 is a perspective view of a portion of turbine exhaust case 30having inner case 34 and outer case 36 with panels 32 therebetween.Although illustrated as containing six panels, the figure is forillustrative purposes and turbine exhaust case 30 may have any number ofpanels 32 as required by design. FIG. 3A is perspective view of aportion of turbine exhaust case 30 illustrated in FIG. 3. The forwardside of inner case 34 is connected to the aft end of inner ring 40,while the forward side of outer case 36 is connected to outer ring 42.Panel 32 extends between inner case 34 and outer case 36. Panel 32contains a hollow airfoil with pressure side 66, suction side 68,leading edge 70, and trailing edge 72. Both pressure side 66 and suctionside 68, as well as leading edge 70 and trailing edge 72, have aradially inner edge (not shown) and radially outer edge, as representedby radially outer edge 74 of pressure side 66. Leading edge 72 has asmooth surface 71 to promote airflow. This smooth surface extends acrossa portion of both pressure side 66 and suction side 68. In someembodiments, this is manufactured as a separate piece and joined to therest of panel 32.

Augmentor spray bar 52 is connected adjacent trailing edge 72 of panel32 at an acute angle to suction side 68. In one embodiment, spray bar 52contains a box structure surrounding the spray nozzles, and has anextension that acts as a flameholder for the exhaust augmentation ofengine 12. Flame tube ring 62 is connected to the aft end of inner case34, and extends to join tailcone 64. In order to reduce the problem ofnegative margin outflow, panel 32 contains a flow diverting structureadjacent leading edge 70.

FIG. 4 is an elevation view of turbine exhaust panel 32. Panel 32 hasleading edge 70 and trailing edge 72, with augmentor spray bar 52attached to trailing edge 72. Also attached to the radially inner edgeis flange 76 with aperture 78. Flange 76 allows attachment of panel 32to turbine exhaust case 30 and the rest of engine 12 by insertion of afastener into aperture 78. Panel 32 also has flanges 80, 82, which alsoaid in locating and securing panel 32 between inner case 34 and outercase 36 in turbine exhaust case 30.

Also illustrated in FIG. 4 are iso-grid supports 38. In this embodiment,the iso-grids 86 a, 86 b, and 86 c contain an arcuate portion adjacentthe radially outer edge and leading edge 70, which act to divert flow offluid passing through the interior of panel 32, and are the flowdiverting structures previously referred to. Additionally, portions ofthe iso-grids that would normally be present and transverse to 86 a, 86b, and 86 c have been eliminated. This creates a more open area forfluid flow, and thus reducing a cause of negative margin outflow, whichmay affect proper cooling of critical area 58. Cooling fluid can moreeasily enter the hollow airfoil and exit film cooling holes 88 toprovide cooling of panel 32. This design allows for greater fluid flowwithout compromising the structural integrity of panel 32. Althoughillustrated as being in the critical area, this new arrangement ofiso-grids 38 can be expanded to any portion of panel 32.

FIG. 5 is a plan view of a portion of turbine exhaust case 30 withturbine exhaust panel 32 containing fluid scoop 90. FIG. 6 is across-sectional view of turbine exhaust case 30 with turbine exhaustcase panel 32 that contains fluid scoop 90. In this embodiment, a pieceof material is formed to create fluid scoop 90 and attached adjacent theradially outer leading edge, which was previously noted as the criticalarea. The fluid scoop is a flow diverting structure that directs fluidflow into an area of the airfoil that lacks sufficient internal pressurefor cooling fluid flow. As illustrated in FIG. 6, fluid scoop 90 isattached to panel 32 and may extend past inner case 34 into fluidpassage 56. This assures that fluid scoop is in contact with fluid F andcan divert some of the flow into the critical area of panel 32. In analternate embodiment, fluid scoop 90 is contained entirely within panel32, and extends from the radially outer edge of the airfoil towards theradially inner edge.

As illustrated in FIG. 5, fluid scoop 90 is connected to flow inhibitor92. Flow inhibitor 92 is a rigid structure 32 that prevents the throughflow of fluid within panel 32. The combination of fluid scoop 90 andflow inhibitor 92 provide internal pressure recovery for panel 32 inarea adjacent flow inhibitor 92. In the embodiment illustrated, flowinhibitor 92 is comprised of two legs that form a right angle. In otherembodiments, flow inhibitor 92 may be a straight piece running at anangle through panel 32, or may be an arcuate segment. Flow inhibitor 92may entirely close off all fluid flow in panel 32. In an alternateembodiment, flow inhibitor 92 permits a limited flow of fluid in thearea adjacent flow inhibitor 92.

With either of the above embodiments for a flow diverting device (fluidscoop 90 or arcuate isogrids 86 a-86 c), sufficient internal staticpressure is created in critical area 58. The flow diverting devicesprevent insufficient internal pressure that leads to a negative outflowmargin in panel 32.

With the above embodiments of a TEC panel with a flow divertingstructure, a method of reducing unfavorable outflow margin in thecooling flow of a turbine exhaust case is possible. First, turbineexhaust gases are directed to a plurality of hollow airfoils within theturbine exhaust case. Next, cooling bypass flow is directed to a radialouter side of the turbine exhaust case. A flow diverting structure isthen provided adjacent a leading edge of one of the plurality of hollowairfoils. The flow diverting structure directs fluid flow into an areaof the airfoil that lacks sufficient internal pressure for cooling fluidflow. This flow diverting structure may be either a fluid scoop asdescribed, a modification of the iso-grid supports as described, or acombination thereof.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A turbine exhaust case panel for use in a gas turbine engine exhaustcase that has a cooling bypass fluid flowing adjacent the exhaust case,the turbine exhaust case panel comprising: an airfoil section; and aflow diverting structure adjacent to a leading edge of the airfoilsection, wherein the flow diverting structure directs a portion of thebypass cooling fluid into an area of the airfoil that lacks sufficientinternal pressure for cooling fluid flow.
 2. The turbine exhaust panelof claim 1 wherein the flow diverting structure comprises: a pluralityof curved iso-grids located on the interior of the airfoil and adjacentto the leading edge of the airfoil.
 3. The turbine exhaust panel ofclaim 1 wherein the flow diverting structure comprises: an air scoopattached to the radially outer edges of a pressure side and a suctionside.
 4. The turbine exhaust panel of claim 3 further comprising: a flowinhibitor contained within the airfoil section that is connected to theair scoop.
 5. The turbine exhaust panel of claim 1 further comprising: aplurality of cooling holes in at least one of a pressure side and asuction side of the airfoil.
 6. The turbine exhaust panel of claim 1further comprising: an augmentor spray bar attached proximate to atrailing edge of the airfoil.
 7. The turbine exhaust panel of claim 1further comprising: at least one flange for connecting the panel to theturbine exhaust case, the flange extending from either a radially inneredge or a radially outer edge of either a pressure side or a suctionside.
 8. A turbine exhaust case comprising: a forward outer diameterring; a forward inner diameter ring; an outer diameter case attached tothe outer diameter ring, wherein a bypass cooling fluid travels adjacentthe outer diameter case; an inner diameter case attached to the innerdiameter ring; a flame tube attached to an aft end of the inner diametercase; and a plurality of airfoils mounted between the inner diametercase and outer diameter case, wherein at least one of the plurality ofairfoils having a flow diverting structure adjacent the leading edge andthe outer diameter ring, and wherein the flow diverting structuredirects a portion of the bypass cooling fluid into an area of theairfoil that lacks sufficient internal pressure for cooling fluid flow.10. The turbine exhaust case of claim 8 wherein at least one airfoilfurther comprises a plurality of iso-grid supports on an interior of theairfoil.
 11. The turbine exhaust case of claim 10 wherein the flowdiverting structure comprises: a curved portion of at least one of theiso-grids adjacent the leading edge.
 12. The turbine exhaust case ofclaim 8 wherein the flow diverting structure comprises: an air scoopattached to the inner ring.
 13. The turbine exhaust case of claim 8further comprising: a trailing edge panel attached to a trailing edge ofthe airfoil and mounted between the inner case and outer case, thetrailing edge panel being mounted at an acute angle with respect to thesuction side of the airfoil.
 14. The turbine exhaust case of claim 13further comprising: an augmentor spray bar attached adjacent thetrailing edge panel.
 15. The turbine exhaust case of claim 8 furthercomprising: a plurality of cooling holes in either a pressure side or asuction side of the airfoil.
 16. A method of reducing unfavorableoutflow margin in the cooling flow of a turbine exhaust case, the methodcomprising: directing turbine exhaust gases to a plurality of hollowairfoils within the turbine exhaust case; directing a cooling bypassflow to a radial outer side of the turbine exhaust case; providing aflow diverting structure adjacent a leading edge of at least one of theplurality of hollow airfoils, wherein the flow diverting structuredirects fluid flow into an area of the airfoil that lacks sufficientinternal pressure for cooling fluid flow.
 17. The method of claim 16further comprising: directing a portion of the cooling bypass flow intothe hollow airfoils.
 18. The method of claim 16 further comprising:providing cooling holes in the hollow airfoils to provide film coolingof the airfoil outer surfaces.
 19. The method of claim 16 wherein theflow diverting structure is an iso-grid on the interior of the at leastone airfoil, the iso-grid containing an arcuate portion adjacent aleading edge of the airfoil.
 20. The method of claim 16 wherein the flowdiverting structure is an air scoop adjacent the leading edge of theairfoil and extends past the outer radial outer side of the turbineexhaust case.